Sense of Sight: A Quick Look

The eye is a round object and is filled with fluid. At the back of the eye is the optic nerve which is responsible for sending the signals to the brain.

The sclera is the outside layer of the eye and is responsible for its shape. This same layer, at the front of the eye, is called the cornea, which allows for light to pass through.

The choroid is the second layer and contains blood vessels. At the front of the eye the choroid contains the ciliary body (controls the size of the lens), and the iris (adjusts around the black pupil).

The retina is the innermost layer and it is the part that senses light. The retina contains rod cells (which look after vision when there is little light), and cone cells (which look after color vision). The macula is an area in the centre of the retina, and in the centre of the macula is the area called fovea centralis which contains cones which are responsible for details. When there is little light details and color are very hard to make out.

The canal of Schlemm is a small canal which allows the fluid inside the eye drain. Since new fluid is created all the time, this is necessary as fluid would otherwise would build up and cause what's called glaucoma.

Conjuctiva is the membrane that protects the eye and keeps it moist. The lacrimal glands, located above the outer sections, produce tears which help clean the outer surface of the eye.

The eye can move in every direction and it is able to do this because of 6 major muscles that attach to the sclera. These muscles are:

Superior rectus: raises the eye.

Inferior rectus: lowers the eye.

Superior and inferior obliques: eye rotation.

Medial rectus: inwards to towards the centre.

Lateral rectus: outwards.

Blindness can be caused by many things, such as:
Glaucoma, when the fluid inside the eye (aqueous humor) does not drain properly and pressure builds up inside the eye. Medication and surgery are used for treatment.
Cataracts: a cloudy film builds over the eye. More likely to occur with age. Surgery can correct this problem.